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Title: High-pressure study of dravite tourmaline: Insights into the accommodating nature of the tourmaline structure

Abstract

The high-pressure behavior of dravite tourmaline [Na(Mg 3)Al 6(Si 6O 18)(BO 3) 3(OH) 3(OH)] has been studied using luminescence spectroscopy and synchrotron-based single-crystal diffraction up to ~65 and ~24 GPa, respectively. Two emission bands associated with Cr 3+/V 2+ substitution are constant in energy up to ~9.0 GPa, and they shift to longer wavelength at higher pressures, suggesting that a change in compressional mechanism could occur at this pressure. Single-crystal diffraction data show subtle changes in ring ditrigonality occur near 9.0 GPa, which could cause the observed change in luminescence. Near 15 GPa, a splitting of one of the emission bands is observed, suggesting that a phase transition occurs at this pressure and that two unique octahedral sites are present in the high-pressure phase. Hysteresis is not observed on decompression, which indicates that this is a second-order transition, and the high-pressure structure appears to be metastable up to ~65 GPa. Single-crystal diffraction measurements show that a phase transition from rhombohedral R3m to rhombohedral R3 occurs at pressures near 15.4 GPa. The high-pressure phase is characterized by a distorted Si 6O 18 ring (e.g., the Si-Si-Si angles deviate from 120°), and the Si, Al, O6, O7, and O8 sites of themore » low-pressure phase split, implying that the high-pressure phase of tourmaline is a higher entropy phase. The large X-site exerts the primary control on compressibility, and the substitution of larger cations into this site will likely lower the pressure at which this transition occurs. Dravite tourmaline shows anisotropic compression with the c-axis being more compressible than the a-axis. The pressure and volume data up to ~15.4 GPa were fit with second- and third-order Birch-Murnaghan equations of state. We obtain a bulk modulus, K 0 = 109.6(3.2) GPa, and a pressure derivative, K 0' = 4.6(8) GPa, and with the pressure derivative set to 4, a bulk modulus of 112.0(1.0) GPa is derived. Moreover, our high-pressure results show that massive overbonding of the X and Y sites can be accommodated by the tourmaline structure. Finally, this unexpected result may explain the extraordinary structural tolerance with respect to chemical substitution on the X, Y, and Z sites.« less

Authors:
 [1];  [2];  [3];  [4]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Physics Division
  2. Univ. of California, Santa Cruz, CA (United States). Dept. of Earth and Planetary Sciences; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
  4. Univ. of California, Santa Cruz, CA (United States). Dept. of Earth and Planetary Sciences
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC)
OSTI Identifier:
1542333
Alternate Identifier(s):
OSTI ID: 1479056
Report Number(s):
LLNL-JRNL-747437
Journal ID: ISSN 0003-004X; 898955
Grant/Contract Number:  
AC52-07NA27344; AC02-05CH11231
Resource Type:
Accepted Manuscript
Journal Name:
American Mineralogist
Additional Journal Information:
Journal Volume: 103; Journal Issue: 10; Journal ID: ISSN 0003-004X
Publisher:
Mineralogical Society of America
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES

Citation Formats

O'Bannon, Earl, Beavers, Christine M., Kunz, Martin, and Williams, Quentin. High-pressure study of dravite tourmaline: Insights into the accommodating nature of the tourmaline structure. United States: N. p., 2018. Web. doi:10.2138/am-2018-6486.
O'Bannon, Earl, Beavers, Christine M., Kunz, Martin, & Williams, Quentin. High-pressure study of dravite tourmaline: Insights into the accommodating nature of the tourmaline structure. United States. doi:10.2138/am-2018-6486.
O'Bannon, Earl, Beavers, Christine M., Kunz, Martin, and Williams, Quentin. Mon . "High-pressure study of dravite tourmaline: Insights into the accommodating nature of the tourmaline structure". United States. doi:10.2138/am-2018-6486. https://www.osti.gov/servlets/purl/1542333.
@article{osti_1542333,
title = {High-pressure study of dravite tourmaline: Insights into the accommodating nature of the tourmaline structure},
author = {O'Bannon, Earl and Beavers, Christine M. and Kunz, Martin and Williams, Quentin},
abstractNote = {The high-pressure behavior of dravite tourmaline [Na(Mg3)Al6(Si6O18)(BO3)3(OH)3(OH)] has been studied using luminescence spectroscopy and synchrotron-based single-crystal diffraction up to ~65 and ~24 GPa, respectively. Two emission bands associated with Cr3+/V2+ substitution are constant in energy up to ~9.0 GPa, and they shift to longer wavelength at higher pressures, suggesting that a change in compressional mechanism could occur at this pressure. Single-crystal diffraction data show subtle changes in ring ditrigonality occur near 9.0 GPa, which could cause the observed change in luminescence. Near 15 GPa, a splitting of one of the emission bands is observed, suggesting that a phase transition occurs at this pressure and that two unique octahedral sites are present in the high-pressure phase. Hysteresis is not observed on decompression, which indicates that this is a second-order transition, and the high-pressure structure appears to be metastable up to ~65 GPa. Single-crystal diffraction measurements show that a phase transition from rhombohedral R3m to rhombohedral R3 occurs at pressures near 15.4 GPa. The high-pressure phase is characterized by a distorted Si6O18 ring (e.g., the Si-Si-Si angles deviate from 120°), and the Si, Al, O6, O7, and O8 sites of the low-pressure phase split, implying that the high-pressure phase of tourmaline is a higher entropy phase. The large X-site exerts the primary control on compressibility, and the substitution of larger cations into this site will likely lower the pressure at which this transition occurs. Dravite tourmaline shows anisotropic compression with the c-axis being more compressible than the a-axis. The pressure and volume data up to ~15.4 GPa were fit with second- and third-order Birch-Murnaghan equations of state. We obtain a bulk modulus, K0 = 109.6(3.2) GPa, and a pressure derivative, K0' = 4.6(8) GPa, and with the pressure derivative set to 4, a bulk modulus of 112.0(1.0) GPa is derived. Moreover, our high-pressure results show that massive overbonding of the X and Y sites can be accommodated by the tourmaline structure. Finally, this unexpected result may explain the extraordinary structural tolerance with respect to chemical substitution on the X, Y, and Z sites.},
doi = {10.2138/am-2018-6486},
journal = {American Mineralogist},
number = 10,
volume = 103,
place = {United States},
year = {2018},
month = {10}
}

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